System of motor control



July 9, 1929. 3 w JQNES 1,720,555

SYSTEM OF MOTOR CONTROL Original Filed Jan. 22, 1926 $13 /5 V4 M mIPA/enter: Ber jamin \A/Jones,

Patented July 9, 1929.

UNITED STATES PATENT OFFICE- BENJAMIN W. JONES, OF SCHENEOTADY, NEWYORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORPORATION OF NEW YORK.

SYSTEM OF MOTOR CONTROL.

Application filed January 2 2, 1926 Serial No. 83,140. -Renewed March18, 1929.

My invention relates 'to improvements in systems of motor control and inparticular to systems for controlling the acceleration of electricmotors.

Time element control of electric motors has certain advantageousfeatures, among which may be mentioned that of requiring the varioussteps of the control to proceed with always at least a certain timebetween the various control steps. However, the ordinary forms of timeelement control leave something to be desired in that the time elementdevice or devices employed are either complicated and expensive or areunreliable. Furthermore, to meet sat1s factorily the conditions imposedby practice in many motor applications, the time intervals between thevarious steps should take into account the current taken by the motor sothat the various steps will not be taken until the motor current hasreduced to at least a predetermined value.

Objects of my invention are the provision of a time element controlwhich takes into account the practical conditions set forth and othersas will be pointed out hereinafter, and the provision of a time elementdevice which is simple, inexpensive and reliable so that the systememploying such a device or a plurality of such devices is simple andreliable.

For an understanding of the invention, reference is had to theaccompanying drawingwhioh shows in very simple diagram a system of motorcontrol embodying the invention.

Referring to the drawing, the electric m0- tor 10 of the three phasealternating current slip ring type is arranged to be connected to thethree phase alternating current supply circuit 11 by means of the linecontactor 12. The acceleration of the motor is controlled by theresistors 13, 14 and 15, which are included in the rotor or secondarycircuit of the motor. The resistor sections 13 are arranged to beshort-circuited by means of the contactor 16, the resistor sections 14by means of the contactor 17, and the resistor sections 15 are arrangedto be short-circuited by means of the contactor 18. The relay 19 isprovided for controlling the energization of the resistor contactor 16,the relay 20 is provided for controlling the resistor contactor 17 andthe relay 21 is provided for controlling the resistor contactor 18.

The relays are substantially identical. in construction and a detaileddescription of the construction and operation of merely the relay 19will be given. The relay operates on the induction disc principle and isprovided with an electromagnet 22 which has a series winding included inthe motor circuit. This electromagnet sets up a flux through the disc 23of non-magnetic material which produces a torque in the disc tendmg torotate the same in the clockwise direction, so as to assist the bias ofthe spindle 24 on which .the disc is mounted. The spindle 24 issupported in any suitable manner, preferably as is common in integratingwattmeters. The clockwise bias of the spindle is provided by means ofthe spring 25 and this insures that with the windings of the relaydeenergized, the switch contact member 26 will be maintained in the openposition against the stop 27. The shunt electromagnet 28 is provided forsetting up a substantially constant flux through the disc 23 forproducing a substantially constant torque in the disc tending to rotatethe same in the counter clockwise direction against the action of theseries electromagnet and the biasing effect of the spring 25. Each ofthe electromagnets 22 and 28 is provided with a pole shader, asindicated, in order to thereby effectively produce the dephased fluxsuitable for effectively setting up the torque in the disc. The disc 23carries a magnetic member 29 which is arranged to be rotated between thepoles of the electromagnet 28, so as to thereby accelerate the closingmovement of the contact 26 and to hold this contact in he closedposition with a substantial 'm'ort applied thereto.

One of the features of the arrangement described is that the controllingrelay is very simple in construction, has relatively few parts which areliable to get out of order and furthermore operates on a general princile which is familiar to electricians charged with the maintenance ofcontrol systems such as the control system of the present invention. Itwill also be observed that the relay will always give a certain minimumtime interval of operation determined by the time required for the-discto rotate from the position indicated in the drawing to the position inwhich the magnetic member 29 is directly between the poles of theelectromagnet 28 when the switch contact 26 is in the closed position.This minimum time interval will be increased, depending upon the currenttaken by the motor, and this effect is produced by means of the serieselectromagnet 22 which exerts a holding effect on the relay proportionalto the current taken by the motor controlled. A further advantageousfeature of the arrangement is that the relays 19, 20 and 21 aremechanically independent of the resistor contactors 16, 17 and 18 andthe line contactor 12 so that these relays may be placed at any suitableposition and enclosed in a casing so as to exclude dust, moisture, andother influences which might have a detrimental effect on the opera-tionof the relays. A further feature of the invention is that by reason ofthe employment of the time element current limit controlling relays, thesystem of control is rendered very simple and effective. While aparticular embodiment of the invention is shown in the control of analternating current motor, the invention is not necessarily limitedthereto, but is applicable to other types of motors as well.

With the various parts of the system in their respective position asindicated in the drawing the operation of my invention is as follows:

In order to connect the motor to the supply circuit and effect theautomatic acceleration thereof, the master switch 30 Wlll be closed,thereby energizing the line contaetor 12 to close and at the same timeenergizing the winding of the shunt electromagnet 28 of the relay 19. Ifthe current taken by the motor 10 is in excess of the predeterminedvalue, the series clectromagnet 22 of the relay 19 will hold the disc 23against the torque set up by the shunt electromagnet 28, but if themotor current drops to the predetermined value, the torque set up by theelectromagnet 28 will predominate over the biasing effect of the spring25 and the holding effect of the series electromagnet 22 so that thedisc will slowly rotate in the counterclockwise direction, carrying theswitch contact 26 toward the closed position. When this movement isnearly completed and the switch contact is nearly in the closedposition, the magnetic member 29 will be nearly within the directinfluence of the flux set up by the shunt electromagnet through thedisc. By reason of the fact that a relatively low reluctance path forthe flux of the electromagnet 28 is thus formed, the torque of theelectromagnet 28 will very greatly predominate over the biasing effectof the spring 25 and the holding effect of the series electromagnet 22and the closing movement of the switch contact 26 will be greatlyaccelerated. This is desirable because the electrical circuit controlledby the contact 26 is quickly closed and arcing at the switch contacts isthereby avoided. Furthermore, a relatively great pressure is applied tothe switch contacts to maintain these contacts in their closed position.

The closing of the contacts controlled by the relay switch member 26will effect the energization of the winding of the resistor contactor 16and this contactor will close, short-circuiting the resistor sections13. The contactor 16 will be maintained closed through an energizingcircuit, independently of the relay 19-th'rough a circuit including theauxiliary switch 31 associated with this contactor. The closing of theresistor contactor 16 will ordinarily cause the motor current toincrease appreciably and the relay 20 will now govern the closing of theresistor contactor 17 in the same manner as the relay 19 controlled theclosing of the resistor contactor 16. The closing of the contacts of therelay 19 not only energized the contactor 16, but also energized theshunt elect-romagnet of the relay 20, thereby rendering this relayeffective to introduce the time element current limit effect, incontrolling the resistor contactor 17. When at least the minimum timehas elapsed and the current taken by the motor has reduced to thepredetermined value, the resistor contactor 17 will be energized toclose andshort circuit the resistor sections 14. The closing of thecontacts of the relay 20 will also energize the shunt electromagnet ofthe relay 21 so as to bring this relay into action to control theresistor contactor 18 in a similar manner to that previously explainedin connection with the relay 19.

It will be observed that with the arrangement heretofore described, thesuccessive closing of the resistor contactors is brought about by thesuccessive energization of the shunt windings of the various relays andthat the series electromagnets of the relay are effective to positivelyhold the relay contacts in their open positions until the rela is set inoperation to produce its time limit current limit effect, by the closingof the preceding relay of the succession or the closing of somepreceding switch of the succession.

lVhat I claim as new and desire to secure by Letters Patent of theUnited States is 1. A system of control for an electric current motorcomprising acceleration controlling means for the motor, and means forcontrolling said acceleration controlling means comprising a devicehaving a rotatable element biased to one position, a winding con-,

nected to be energized in accordance with the motor current for settingup a flux through said element which exerts a torque on said elementproportional to the value of the motor current to hold the element insaid biased position, electroresponsive means for setting up asubstantially constant flux through said element which exerts a countertorque tending to move the element to a second position against the biasthereof and against the holding effect of said winding, the said countertorque predominating to move. the element when the current taken by themotor is less than a predetermined value, whereby a time interval in thecontrol of the motor is had which is always a minimum value and isgreater depending on the current taken by the motor and means comprisingan armature member located at the periphery of said rotatable member forincreasing the counter-torque between said elements and said shuntwinding as the said element approaches said second position.

2. In a system of control for an alternating current motor,electroresponsive acceleration controlling means, and means forcontrolling the energization of said electroresponsive means comprisingan inductive device having a rotatable element biased to a predeterminedposition, a normally open switch contact closed by said element for.

energizing said. electrorcsponsive means, a series winding connected tobe energized in accordance with the motor current for exerting a torqueon said element proportional to the value of the motor current to holdthe element in said biased position, a shunt winding which normally setsup a substantially constant counter torque on said element tending torotate the same and effect the closure of said contact against the biasof said element and the holding effect of said series winding, and meansfor increasing the counter torque set up in said element by said shuntwinding as the said contact approaches the closed position and when saidcontact is in the closed position.

3. In a system of control for alternating current motors, a plurality ofcontactors arranged to be closed in a definite succession forcontrolling the motor, a separate relay for controlling each of aplurality of said contactors to control the speed of the motor, each ofsaid relays having a rotatable element biased to a predeterminedposition, switch contact mechanism controlled by said element forcontrolling the contactor associatcd with said relay, a series windingconnected to be energized in accordance with the motor current forexerting a torque on said clement proportional to the value of the motorcurrent tending to hold the element in said biased position, a shuntwinding which sets up a substantially constant torque on said clementtending to rotate the same to effect operation of said contact mechanismagainst the bias of said element and the holding efi'ect of said serieswinding, the torque of said shunt winding predominating over the bias ofsaid element and the torque of said series winding when the motorcurrent has dropped to a predetermined value, and connections throughwhich the shunt Winding of each relay is energized in retric motorscomprising a disc, a winding arranged to be energized in accordance withthe motor current for setting up a series characteristic torque tendingto rotate the disc in one direction, a second winding for setting up ashunt characteristic torque tending to rotate the disc in the oppositedirection, the torque of said series characteristic windingpredominating over the torque of said shunt characteristic winding whenthe motor current is, above a predetermined value and the torque of saidshunt characteristic winding predominating over the torque of saidseries characteristic winding when the motor current is less than saidpredetermined value, a magnetic armature so mounted on said disk as toincrease the torque between said shunt winding and said disk when thelatter is rotating in said opposite direction, and switch contactscontrolled by said disc for controlling the motor.

5. An electroresponsive acceleration controlling device for alternatingcurrent motors comprising a disc biased to one position, a serieselectromagnet arranged to be energized in accordance with the motorcurrent for setting up a series characteristic torque tending to rotatethe disc in one direction, a shunt electromagnet angularly disposed withreference to said series electromagnet for setting up a counter torque1n said disc, the torque of said series electromagnet and the bias ofsaid disc predominating over the torque of said shunt electromagnet whenthe motor current is abovea predetermined value and the torque of saidshunt electromagnet predominating over the torque of said serieselectromagnet and the bias of said disc when the motor current is lessthan said predetermined value, nor-

